This invention relates to housings, and more particularly, to housings that enclose intrinsically-safe electronics.
Electronics for many applications may be required to operate in caustic or potentially explosive environments. The operation of electronics in a potentially explosive environment can result in ignition of volatile material. One solution is to enclose the electronics in an explosion-proof housing isolated from the environment. Making a housing explosion-proof includes issue of encapsulation, pressurization, and flameproof containment. An explosion-proof housing design requires a flame-path of a sufficient length to cool any material escaping from a container if combustion does occur within the housing. Flame-path length is a function of the length of a machined thread. Explosion-proof housings are generally more expensive to fabricate and require additional wall thickness and structural support.
Another solution when electronics are used in volatile environments is to design the electronics to intrinsically-safe standards. Intrinsically-safe electronics operate at a low power level below a particular energy threshold. Operating a device at a low power level ensures that heat or spark generation will not occur. The power-level requirements for intrinsically-safe electronics are established by regulatory agencies such as the Underwriters Laboratory (UL) in the United States, CENELEC in Europe, CSA in Canada and TIIS in Japan.
When intrinsically-safe electronics are operated in a caustic or volatile environment, it is necessary to protect the electronics in a housing to prevent circuit damage or failure. A problem with housings for intrinsically-safe electronics is that the housing must be sealed to prevent environmental intrusion. It is also desirable that a housing for intrinsically-safe electronics be modular and interchangeable so that housing parts can be mass-produced. A housing may be formed using one or more members that are combined to form an enclosure that contains the electronics. There is a cost advantage to using intrinsically-safe electronics instead of explosion-proof designs because of the less stringent requirements for an intrinsically-safe electronics housing. However, prior methods of assembling the members used to form a housing for intrinsically-safe electronics are virtually identical to the methods used for explosion-proof housings. Methods for assembling the members could include bolting, welding, or affixing via a threaded fitting. However, each of these methods of assembling has cost, manufacturing, or logistical limitations that render such methods undesirable, and which offset the cost savings of an intrinsically-safe design. Actual cost-benefits depend upon finding a solution for assembling and sealing parts of a housing that is as robust and reliable as prior methods, and also allows rapid precision alignment of parts, but does not require precision machining.
One application for electronics that operate in a volatile environment is a Coriolis flowmeter. A Coriolis mass flowmeter measures mass flow and other information of materials flowing through a pipeline in the manner described by U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. A Coriolis mass flowmeter has one or more flow tubes of a curved or straight configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Pickoffs are placed at two different points on the flow tube to produce sinusoidal pickoff signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the pickoffs is calculated in units of time. The phase difference between the two pickoff signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
The sensors transmit the sinusoidal signals to meter electronics. The meter electronics generates parameter signals that indicate properties of the material flowing through the flowmeter. The meter electronics also generates a drive signal applied to the driver to vibrate the flow tubes. The parameter signals are then transmitted to a host system which provides the desired properties to a user.
Coriolis flowmeters have inherent power requirements necessary for ordinary operation that generally have required conformance to explosion-proof designs. In the prior art, the standard practice has been to design flowmeters to explosion-proof standards. An explosion-proof design requires that the meter electronics be contained in an explosion-proof container, which typically encompasses the entire flowmeter. Another method of the prior art removes the meter electronics from the flowmeter and into another housing that is explosion-proof, but attached to the flowmeter. This method requires that the meter electronics housing comply with all appropriate mandates for an explosion-proof design, which includes precision thread machining of fitted members of the housing for proper flame path length. Precision thread machining is expensive, and is easily damaged under normal use. Additionally, machining of parts contributes a step to the manufacturing process, adding time to fabrication and also increasing costs.
Another method is to use intrinsically-safe electronics in a separate housing for the meter electronics. This method allows the use of housings designed to the more relaxed intrinsically-safe housing requirements. The primary advantage of the intrinsically-safe design approach is the application of less stringent housing requirements. However, in the prior art the cost of attaching and sealing parts to form enclosures for this purpose has not provided a commercial benefit because of the cost of manufacture. A method for enclosing electronics meeting intrinsically-safe standards is desired that provides a rapid, effective, robust, and reliable means for sealing multiple members of a housing as well as prior methods while providing ease of manufacture and cost savings.
The above and other problems are solved and an advance in the art is achieved through the provision of a cam-lock assembly for affixing and sealing members of a housing for containing intrinsically-safe electronics. The first distinct advantage of the present invention is the ability to cast a cam-lock feature, thereby avoiding the expense of precision machining after casting as in threaded attachment methods. A second distinct advantage of the present invention is the ease of coupling and sealing members used to form a housing for intrinsically-safe electronics. Members of a housing may be attached or detached with ease using a twisting action as in threaded assemblies. Another feature of the cam-lock is that members may have one of several predetermined orientations when coupled simply by casting multiple cam-lock features into the members.
In one example of the invention, the housing comprises a first member, a second member, a seal, and electronics. The first member has a body comprised of a first end portion and a second end portion. The first end portion of the first member comprises at least one pin protruding from the first end portion of the first member. The second member has a body and a cavity, with the body comprised of a first end portion and a second end portion. The first end portion of the second member is configured to mate with the first end portion of the first member. The first end portion of the second member comprises at least one groove configured to engageably receive the pin of the first end portion of the first member. The seal is configured to fit between the first member and the second member. The electronics is configured to mount within the cavity of the second member. Advantageously, the first member can be cast with the pin and the second member can be cast with the groove. The first and second members do not have to be machined any further, which would be the case if the first and second members were threaded. Therefore, the housing does not required as much precision machining which cuts down on time and cost.
Another example of the invention involves a method for sealing the electronics within the housing. The method begins by mounting the electronics within the cavity of the second member. The method also includes positioning the seal between the first member and the second member. The method also includes mating the first end portion of the second member with the first end portion of the first member. The method also includes rotating the first member and the second member in opposing directions relative to one another thereby sliding the pin of the first end portion of the first member into the groove of the first end portion of the second member. With the second member and first member joined and the pin slid into the groove, the housing forms an intrinsically-safe housing. The combination of the pin and the groove can be considered a cam-lock system.
In another example of the invention, the housing further includes a third member. The third member comprises a body having a first end portion and a second end portion. The first end portion of the third member comprises at least one pin protruding from the first end portion. The pin of the first end portion of the third member is configured to engage with a groove on the second end portion of the second member. The third member also includes a mount. The mount is configured to affix the third member to another surface, such as a surface on a Coriolis flowmeter.
In another example of the invention, the first member includes a cavity within the body of the first member. The first member also includes a user interface mounted in the cavity. The user interface is configured to communicate with the electronics mounted in the second member to provide an interface between an operator and the electronics. In another example of the invention, the housing further includes wiring and an opening in either the first member or the second member. The wiring connects to the electronics and extends from inside the cavity of the second member and through the opening to outside of the housing.
One aspect of the invention includes a housing, comprising:
a first member having:
a body comprised of a first end portion and a second end portion, said first end portion of said body of said first member comprising at least one pin protruding from said first end portion of said body of said first member;
said housing further comprising a second member having:
a body comprised of a first end portion and a second end portion, said first end portion of said body of said second member configured to mate with said first end portion of said body of said first member, said first end portion of said body of said second member comprising at least one groove configured to engageably receive said at least one pin of said first end portion of said body of said first member, and
a cavity within said body of said second member;
said housing further comprising a seal configured to fit between said first member and said second member; and
said housing further comprising electronics configured to mount within said cavity of said second member.
Another aspect of the invention includes a housing wherein said second end portion of said body of said first member comprises:
an end surface affixed to said body of said first member that encloses said second end portion of said body of said first member.
Another aspect of the invention includes a housing wherein said end surface comprises a gripping surface on said end surface.
Another aspect of the invention includes a housing wherein said body of said first member comprises:
a cavity within said body of said first member; and
a user interface mounted in said cavity within said body of said first member and configured to communicate with said electronics.
Another aspect of the invention includes a housing wherein:
said first end portion of said body of said first member is substantially circular; and
said first end portion of said body of said second member is substantially circular.
Another aspect of the invention includes a housing wherein:
said at least one pin protrudes from an inner surface of said first end portion of said body of said first member toward the center of said first member; and
said at least one groove extends along an outer surface of said first end portion of said body of said second member.
Another aspect of the invention includes a housing wherein:
said at least one pin protrudes radially from an outer surface of said first end portion of said body of said first member; and
said at least one groove extends along an inner surface of said first end portion of said body of said second member.
Another aspect of the invention includes a housing further comprising:
a wave washer configured to fit between said first member and said second member.
Another aspect of the invention includes a housing wherein:
said first end portion of said body of said first member comprises four pins protruding from said first end portion of said body of said first member; and
said first end portion of said body of said second member comprises four grooves configured to engageably receive said four pins of said first end portion of said body of said first member.
Another aspect of the invention includes a housing further comprising:
a third member having:
a body comprised of a first end portion and a second end portion, said first end portion of said body of said third member configured to mate with said second end portion of said body of said second member, said first end portion of said body of said third member comprising at least one pin protruding from said first end portion of said body of said third member;
said second end portion of said body of said second member comprising at least one groove configured to engageably receive said at least one pin of said first end portion of said body of said third member.
Another aspect of the invention includes a housing wherein said third member further comprises a mount configured to affix said second end portion of said body of said third member to a Coriolis flowmeter.
Another aspect of the invention includes a housing wherein said second member comprises a mount configured to affix said second end portion of said body of said second member to a Coriolis flowmeter.
Another aspect of the invention includes a housing wherein said electronics comprises meter electronics for a Coriolis flowmeter.
Another aspect of the invention includes a housing wherein said at least one groove of said first end portion of said body of said second member comprises a detent at an end of said at least one groove.
Another aspect of the invention includes a housing wherein said seal comprises an O-ring.
Another aspect of the invention includes a housing further comprising:
wiring connected to said electronics; and
an opening in one of said first member or said second member for said wiring to extend from inside said cavity to outside said cavity.
Another aspect of the invention includes a method for sealing said electronics in the housing, said method comprising the steps of:
mounting said electronics within said cavity of said second member;
positioning said seal between said first member and said second member;
mating said first end portion of said body of said second member with said first end portion of said body of said first member; and
rotating said first member and said second member in opposing directions relative to one another thereby sliding said at least one pin of said first end portion of said body of said first member into said at least one groove of said first end portion of said body of said second member.
Another aspect of the invention includes the step of positioning a wave washer between said first member and said second member prior to mating said first end portion of said body of said second member with said first end portion of said body of said first member.
Another aspect of the invention includes the step of mounting said second end portion of said body of said second member to a Coriolis flowmeter.
Another aspect of the invention includes the step of connecting said electronics to a Coriolis flowmeter.